The invention relates to an air pipe head for venting a tank of a vessel, such as a ballast tank, an oil tank, a fresh water tank or a sewage tank.
When a tank of a vessel is filled with a liquid, it needs to be vented to allow air to escape from the tank as the tank is filled. Also, in many cases, one or more vents that are provided for this purpose also need to be capable to operate as overflow passages, to allow liquid to escape when a tank is filled to its full capacity, to protect the pumps and the tank from damage. Conversely, when a tank is emptied, the vent provides for a passage that allows air to enter the tank to take up the volume left by the discharged liquid. Furthermore, the vents allow air to flow in and out of the tank to equalize pressure difference due to variations in temperature.
For vents having an outer opening at a deck of a vessel or otherwise exposed to waves, it has to be ensured that no or no significant volumes of splash water can enter the vent even when exposed to heavy weather along with a lot of splash water or even waves running over the deck. An example of such an air pipe head according to the introductory portion of claim 1 is known from Dutch patent 1014531. Such an air pipe head has a housing bounding a venting channel and a chamber, wherein the venting channel has an end port opening downwards into the chamber. A float member is arranged in the chamber and guided for guided movement between an uppermost position closing off the end port and a lowermost position spaced below the end port. The chamber communicates with surroundings of the air pipe head via at least one side port. If splash water or a wave runs over the deck and into the chamber towards the end port, the float member is caused to float up against the end port and temporarily closes off the end port to prevent water from entering, until the water has flowed away and the float descends back to its lowermost position again leaving the end port of the vent free. Depending on the extent to which the entry of water through the pipe head must be avoided, the side ports may have an upper end that is above or near the upper end of the float in its lowermost position for achieving high flow rates or have an upper end at a much lower level, for instance below a center of the float in its lowermost position or near the lower end of the float in its lowermost position to more effectively shield the end port from water ingress.
In many applications, an important characteristic of such air pipe heads is the flow rate of air into the tank, so that the tank can be emptied quickly, and the flow rate of liquid out of the tank so that no damage occurs even when the tanks is filled at a high flow rate until it flows over via the vents. Arranging the upper contour of the side ports lower will generally go at the expense of achievable flow rates.